Controlled release dosage forms are well known, including solid dosage forms incorporating one or more active ingredients in addition to lubricants, carrier bases, fillers and other excipients, wherein the carrier base may be a hydrophillic, hydrophobic or water-insoluble polymer.
The mechanism by which controlled release dosage forms act to disperse the active ingredients over a period of time have been described at length in the literature. See for example, Manford Robinson, Chapter 14, "Sustained Action Dosage Forms", The Theory and Practice of Industrial Pharmacy, 2nd ed., ed. L. Lachman, H. Lieberman and J. Kanig (Philadelphia; Lea & Febiger, 1976). The various advantages of controlled release dosage forms are well known to those skilled in the art, e.g., the therapeutic advantages of sustained blood levels and better patient compliance, and the advantages of being able to use smaller dosage units and/or higher dosages per unit which make the dosage forms easier to administer and more economical to manufacture.
The use of HPMC 2910 has previously been disclosed, for example, by Christensen and Dale in U.S. Pat. No. 3,065,143, wherein at least one third of the weight of a controlled release tablet had to be HPMC USP 2910, and by Schor et al. in U.S. Pat. No. 4,389,393, wherein a hydroxypropylmethylcellulose having a methoxyl content of 16-24 weight-% and a number average molecular weight above 50,000 may be combined with HPMC USP 2910.